This invention relates to fluidic proximity sensors.
A variety of fluidic proximity sensors are known in the prior art. In general, such sensors comprise a tube within a tube, the tubes being so sized as to provide an annular passageway therebetween. In operation, air is introduced into the annular passageway and exists at the end of the device. The presence of an object near the exit end causes some portion of the air to be directed into the bore of the inner tube, serving as a signal to indicate the presence of the object.
For many applications, the design and operating characteristics of the sensor are not critical. Increasingly, however, attention has been directed to improving the operation. Principal efforts in this regard are directed to improved recovery ratios and the ability to sense at increased distances.
The recovery ratio of such a sensor is defined as the ratio of the supply pressure to the signal pressure with a given object at a given spacing from the sensor. Obviously improving the ratio provides the opportunity to reduce air pressure and usage and/or to increase the sensing signal level.
The distance at which the sensor can reliably detect an object is of obvious importance is related, in most cases, to the recovery ratio. In addition some applications require a device with a signal pressure versus distance from sensed object characteristic curve which exhibits a sharp on-off change at a particular distance.
A further desirable characteristic of a fluidic sensor is the ability to sense small or irregularly shaped objects at reasonable distances. The known prior art devices are not generally satisfactory in this regard.
While some improvement in these areas has been achieved still more sensitive devices are desired for some applications. Also, at least some of the more sensitive devices now available are very complex and expensive, limiting their appeal.
It is, therefore, an object of the present invention to provide a proximity sensor with an extremely high recovery ratio.
It is a further object of the invention to provide such a device with a sharp on-off response characteristic.
It is another object of the invention to provide a sensor which can reliably detect small or irregular objects.
It is still a further object of the invention to provide such a device which is relatively simple in design and therefore easy to produce.